Whenever his Manchester City side have played Liverpool in the past, Pep Guardiola has always had a pretty good idea of what to expect from the Reds.
In the past two or three seasons, there have been a few question marks over who should play alongside Virgil van Dijk at the back, or which combination Jurgen Klopp would go with in midfield.
Liverpool’s front three of Sadio Mane, Roberto Firmino and Mohamed Salah never changed, though.
That trio have started all eight games between the two teams in the Premier League or Champions League since Salah moved to Anfield in summer 2017, scoring 10 goals between them.
Sunday could be a different story because of the spectacular form of Diogo Jota, who has scored six goals in Liverpool’s past four games and could displace Firmino from that talented trio.
It is Klopp who has to make that decision but whoever he goes with will give City a different kind of problem to solve, because it will change the way that the Reds defend and attack.
When Liverpool are under the cosh and want to relieve the pressure, then Firmino is ideal for helping them get the ball up the pitch. He doesn’t have blistering pace, but he is brilliant at building moves.
Like the Brazilian, Jota is excellent at pressing too, but he is more of a counter-attacking player, who can go at teams at speed like Mane or Salah, and he also makes Liverpool’s attack more interchangeable.
With Firmino in the team, you know where each of the three is playing. I know he does wander into wide areas but generally he drops deeper into central midfield, with Mane on the left and Salah on the right.
When Jota plays, we have seen him operating out on the left wing, with Mane more central and Salah still on his flank but with all three of them staying high up the pitch.
That forces the opposition full-backs to stay back, because they are petrified of their pace, which could be important on Sunday.
We know City duo Kyle Walker and Joao Cancelo like to get forward but will they take that risk against the Reds? They are the home team, but they will have to be very careful.
Why we won’t see the Reds field a Fab Four
I still thought Firmino would start against City, right up until Jota scored that brilliant Champions League hat-trick against Atalanta on Tuesday.
Now everyone is guessing about who will get the nod, including Guardiola. City will have had to prepare for facing both options in training this week.
One thing I don’t see Klopp doing is playing Jota and Firmino plus Mane and Salah at Etihad Stadium, like he did against Sheffield United at the end of October.
It didn’t quite work in attack having all four of them on the field at the same time, and the 4-2-3-1 formation that Klopp used that day left them vulnerable in wide areas too.
Yes, having a front four makes it easier to press but if City get past them, Liverpool are potentially leaving their full-backs facing two-on-one situations if Walker or Cancelo fly forward and one of their two holding midfielders cannot get across to help out.
I can’t see Klopp allowing that to happen on Sunday. Whoever he goes with up front, he will want three men in his midfield to sit in and protect his defence a bit more.
City have fast forwards of their own
We know what City will do defensively, and go with Ruben Dias and Aymeric Laporte as their centre-halves. Along with Walker and Cancelo, they have looked solid together so far but this game will be their biggest test yet.
Guardiola does have a choice to make in attack now Gabriel Jesus is fit again, but I am expecting Ferran Torres to continue in the middle of their front three.
Jesus only played his first 20 minutes since 21 September when he came off the bench to score against Olympiakos on Tuesday and, with Torres adapting well to his new role, there is no need to use the Brazilian unless it is absolutely necessary.
Like Liverpool when Jota is in the side, City’s front three is very versatile and able to switch positions easily.
Whether it is Jesus or Torres who starts alongside Raheem Sterling and Riyad Mahrez they will be a real handful for Liverpool, who are still trying to form a settled defensive unit without the injured Van Dijk.
How will they handle them? Well, if Joel Matip is not fit enough to return then I think Nat Phillips gets the nod alongside Joe Gomez at the back.
Facing City’s fast forwards will be a very different challenge to dealing with West Ham’s more methodical attacks, which Phillips did so well with last week.
He won a lot of high balls in the box from crosses against the Hammers but City don’t really play many of those, even from set-pieces. They prefer to pass their way into the box and play low balls across goal when they get there.
Phillips will have to adapt his game but it is not just City who play with nippy front players so it is something he will have to get used to as a Premier League defender.
I am sure he came up against some quality strikers in his time on loan in Germany earlier this year but probably the best preparation for what he can expect on Sunday will have come in training when he has faced his own forwards, which is a frightening enough prospect for anyone.
Both teams are vulnerable at the back
Liverpool’s defence has been much better since Alisson returned in goal, but they will always allow sides some opportunities because they are so attack-minded themselves.
City have their own vulnerabilities at the back for similar reasons, and I don’t think they are anywhere near their brilliant best going forward either, despite winning their past three games.
I was at the Etihad on Tuesday for BBC Radio 5 Live alongside John Murray, who was spot on when he said that City did against Olympiakos what they have done in most games this season – which is make a really strong start and smother teams for 20 minutes or so, but then drop off.
There are doubts over Liverpool too, even if I did see their 7-2 defeat by Aston Villa as just a really bad day at the office and, when you put all of that together, this game feels far less decisive than some of their recent meetings.
In November last year, Liverpool beat City at Anfield in what was seen as a huge step towards them winning the title, and not just because it saw them open up a nine-point lead over their biggest rivals after winning 11 of their first 12 games.
This time around, another Reds win would see them move eight points above City, who have got a game in hand, but I don’t think it would be seen as being such a defining one for their season.
The same goes if Guardiola’s side take the points because there are plenty more tough battles ahead for both sides.
Teams don’t fear City like they used to because they have seen how you can beat them, and the same is happening with Liverpool now too.
I still believe Klopp’s side will successfully defend their title, but this season already feels very different to the last one when they were runaway champions.
Stephen Warnock was speaking to BBC Sport’s Chris Bevan.
- Watch 13 first-round ties on BBC iPlayer and the BBC Sport website and app this weekend. Find out more here.